Retransmission ordering method, wireless communication system, receiver and transmitter

ABSTRACT

A wireless communication system wherein frame data is encoded with an outer code and then divided into predetermined number of blocks which are encoded with an inner code into transmission data. In a receiver, a decoder decodes the received transmission data in accordance with the inner code, a retransmission order determining unit determines whether to perform a retransmission order in units of blocks based on the likelihood information (decoded soft-decision value). At this time, the retransmission order determining unit inhibits the retransmission order for the block if the number of inner-code errors in a frame consisting of predetermined number of blocks stays within a limit of what the outer code can correct at a decoder and determines that a retransmission is necessary if the number of inner-code errors in the frame exceeds the limit.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2004-082118 filed in the Japanese Patent Office on Mar.22, 2004, the entire contents of which being incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a wireless communication system forperforming error correcting coding to which an outer code and an innercode are applied. More particularly, it relates to a Hybrid ARQtechnique for composing and decoding retransmission data.

BACKGROUND OF THE INVENTION

In a case where a communication channel is degraded in a wirelesscommunication system, retransmission control is performed so thatcommunication channel errors decrease. This is known as a name of ARQ(Automatic Repeat reQuest). In an ARQ scheme, a receiver cancelserroneous data and requests a transmitter to retransmit the same data.

As an extension of an ARQ technique, there is a Hybrid ARQ techniquewhich incorporates retransmission processing and encoding (errorcorrecting coding) (see Japanese Patent Laid-Open No. 2002-171245). TheHybrid ARQ technique is such that erroneous data prior to decoding isstored and decode processing is performed after the erroneous data isadded to retransmission data received thereafter, for the sake ofeffective reuse of the signal component included in the precedingerroneous data.

FIG. 9 is a block diagram showing an exemplary configuration of atransmitter 300 for realizing a conventional retransmission scheme.

An error detecting code unit 301 adds an error detecting code to userdata. The error detecting code includes typically Cyclic RedundancyCheck (CRC). Next, an encoder 302 encodes the data, providing redundancyfor the data. This encoding uses typically a convolutional code or aturbo code. The data encoded by the encoder 302 is temporarily stored ina retransmission buffer 303. A modulator 304 modulates the encoded data,and a transmitting/receiving unit 305 transmits the modulated data astransmission data. The data is converted to a radio frequency band bythe transmitting/receiving unit 305 in the case of wirelesstransmission. A demodulator 306 demodulates the data received from thetransmitting/receiving unit 305, and retransmission control informationis extracted from the demodulated data. If the extracted data is ACK(data correctly received), a retransmission controller 307 clears theretransmission buffer 303 and transmits new data. If the extracted datais NACK (retransmission order), the data in the retransmission buffer303 is modulated again and retransmitted.

FIG. 10 is a block diagram showing an exemplary configuration of areceiver 400, which corresponds to the transmitter 300 of FIG. 9, forrealizing a conventional retransmission scheme. The transmission datareceived by a transmitting/receiving unit 401 is detected anddemodulated by a demodulator 402. Soft-decision data outputted from thedemodulator 402 is temporarily stored in a composition buffer 403. Ifthere exists past transmission data received from the transmitter, thepast transmission data is added to the transmission data and the contentof the composition buffer 403 is updated. A decoder 404 decodes theoutput of the composition buffer 403. An error detector 405 detects anerror of the demodulated and decoded data using the error detectingcode. If the error detector 405 determines that there is no error, theerror detector 405 outputs the user data, clears the composition buffer403, and transmits ACK (data correctly received). The result of theerror detection is sent to a retransmission order controller 406. Theretransmission order controller 406 transmits NACK (retransmissionorder) if an error is detected by the error detector 405.

With the configuration as described, error-free data transmission withless retransmission can be achieved.

On the other hand, there is a scheme for performing error correctingdoubly to improve resistance to transmission line errors. In the schemeas mentioned, a structure in which an outer code corrects an errorproduced in an inner code provides enhanced resistance to transmissionline errors.

FIG. 11 is a block diagram showing an exemplary configuration of atransmitter 500 that uses a scheme for performing error correctingdoubly.

New user data to be transmitted is temporarily stored in aretransmission buffer 501. If data to be transmitted is new data, thetransmitter 500 transmits the stored data. If data to be transmitted isretransmission data, the transmitter 500 transmits the past stored data.An error detecting code unit 502 adds an error detecting code (such asCRC) to transmission data. An encoder 503 encodes the transmission datato which the error detecting code is added, using an error correctingcode of an outer code. A Reed-Solomon code, a Bose-Chaudhuri-Hocquenghemcode (BCH code), etc. are used as the outer code. The data encoded bythe encoder 503 is divided into M blocks at a frame dividing unit 504.An encoder 505 encodes each of the divided data using a second errorcorrecting code of an inner code. A convolutional code, a turbo code,etc. are used as the inner code. The data encoded by the encoder 505 ismodulated by a modulator 506, and the modulated data is transmitted to atransmission line through a transmitting/receiving unit 507. The datareceived by the transmitting/receiving unit 507 is demodulated by thedemodulator 508, and the resulting data is sent to a retransmissioncontroller 509. The retransmission controller 509 extracts aretransmission ordering message from the demodulated data. If themessage is ACK, the retransmission controller 509 clears theretransmission buffer 501 in which the past transmission data is storedand transmits new data. If the message is NACK, the retransmission datastored in the retransmission buffer 501 is transmitted.

FIG. 13 shows schematically a relationship between the frame data andthe divided blocks in the transmitter 500. Frame data 701 is stored inthe retransmission buffer 501, and the error detecting code is added tothe frame data 701. The encoder 503 encodes the frame data 701 using theouter code to make encoded data 702. The frame dividing unit 504 dividesthe encoded data 702 into M blocks 703. The encoder 505 encodes eachdivided block using the inner code to make encoded blocks 704.

FIG. 12 is a block diagram showing an exemplary configuration of areceiver 600 corresponding to the transmitter 500 of FIG. 11.

A signal received by a transmitting/receiving unit 601 is detected anddemodulated by a demodulator 602. A decoder 603 decodes each of thedivided blocks (encoded blocks 704) of the received signal. A framecombining unit 604 combines M blocks of the decoded data and creates adata frame which is further decoded at a decoder 605. An error detector607 determines whether there is an error in the decoded data using theerror detecting code. If there is no error, the error detector 607outputs the decoded data as user data. The retransmission ordercontroller 608 creates ACK if the error detector 607 determines thatthere is no error, or NACK if the error detector 607 detects an error. Amodulator 609 modulates a retransmission control message, and atransmitting/receiving unit 601 transmits the message.

With the configuration as described, resistance to transmission lineerrors can be increased.

However, there is a problem described below in the case where theretransmission scheme is applied to a communication system that containsboth inner and outer codes.

That is, in the case of performing a retransmission order for anouter-code error, data that is determined to have no inner-code error isalso retransmitted; therefore, it does not necessarily lead toimprovement of transmission efficiency.

Further, there may be a case where a retransmission order is performedin units of divided blocks for an inner-code error. In this case, ifretransmission orders are performed for all inner codes, there occursome retransmission orders for errors that can be corrected withouter-code error correction; therefore, it does not lead to improvementof transmission efficiency, either.

SUMMARY OF THE INVENTION

Under the circumstances, the present invention addresses theabove-mentioned problem by providing a retransmission ordering method, awireless communication system, a receiver and a transmitter that canimprove transmission efficiency in the case of performing errorcorrecting coding to which an outer code and an inner code are applied.

One embodiment of the present invention is directed to a retransmissionordering method in a receiver for receiving transmission data bywireless, frame data being encoded with an outer code and then dividedinto predetermined number of blocks which are encoded with an inner codeinto the transmission data. The retransmission ordering method has thesteps of receiving transmission data; storing the received transmissiondata in a buffer; decoding the transmission data stored in the buffer inaccordance with the inner code and outputting a decode result andlikelihood information thereof (decoded soft-decision value); creatingframe data by combining the decoded blocks; decoding the frame data inaccordance with the outer code; determining whether or not to perform aretransmission order in units of blocks based on the likelihoodinformation; and transmitting a retransmission order for an applicableblock if it is determined that a retransmission is necessary accordingto the step of determining whether or not to perform a retransmissionorder. At the step of determining whether or not to perform aretransmission order, the retransmission order for the block isinhibited if the number of inner-code errors in a frame composed of thepredetermined number of blocks stays within a limit of what the outercode can correct and it is determined that a retransmission is necessaryif the number of inner-code errors in the frame exceeds the limit.

In the retransmission ordering method according to the embodiment of thepresent invention, in the case of performing a retransmission order inunits of divided blocks for an inner-code error at the time of receivingtransmission data that are double encoded with outer and inner codes forerror correcting, it is determined based on the likelihood informationwhether or not to perform the retransmission order. More specifically,the retransmission order for the block is inhibited if the number ofinner-code errors in a frame composed of the predetermined number ofblocks stays within a limit of what the outer code can correct and it isdetermined that a retransmission is necessary if the number ofinner-code errors in the frame exceeds the limit. Thus, the receiverdoes not perform retransmission orders for all of the divided blocks forwhich the inner code cannot perform error correcting, but by utilizingerror correction capability of the outer code effectively, theretransmission order for a divided block can be prevented fromoccurring. Therefore, the wasting of wireless communication resourcescan be avoided.

In the step of determining whether or not to perform a retransmissionorder, an average value of absolute values of the likelihood informationwithin a block is calculated as an evaluation value. It can bedetermined whether or not the block needs to be retransmitted bycomparing the evaluation value with a predetermined threshold value.That is, it can be properly determined whether or not the block needs tobe retransmitted by employing a known relationship between theevaluation value and the number of bit errors in the block.

As for the evaluation value, the number of bits that lead to absolutevalues of the likelihood information (decoded soft-decision values) thatare not more than a specified threshold value may be calculated as anevaluation value.

More specifically, an evaluation value corresponding to the number oferrors N/M allocated to each inner code can be the predeterminedthreshold value in the case where error correction capability of theouter code can correct N errors and one piece of frame data is dividedinto M pieces.

The retransmission ordering method, an error detecting code being addedto the frame data which is then encoded with the outer code, may furtherhave the steps of performing error detection for a decode result inaccordance with the error detecting code after frame data obtained bydecoding in accordance with the inner code is decoded in accordance withthe outer code; and changing the predetermined threshold value in unitsof data frames in such a way that the retransmission order for the blockoccurs easily if an error is detected in the step of performing errordetection and in such a way that the retransmission order for the blockhardly occurs if no error is detected. In this way, the predeterminedthreshold value is dynamically changed in units of data frames, andthereby adjusted appropriately in such a manner that an incidence of anouter-code error accords with an operational target of datacommunication.

The retransmission ordering method may further have the step of changingthe predetermined threshold value in units of blocks in a data frameusing a threshold adjustment (initial value: 0) updated by updating thenumber of errors N/M allocated to each inner code, based on the numberof accumulated errors as to sequential blocks in one data frame. Thus,the threshold value can be controlled for each block appropriately inaccordance with an estimated value of quality of the received blocks inan outer-code frame. Therefore, retransmission of unnecessary inner-codeblocks can be avoided.

The retransmission ordering method, an error detecting code being addedto the frame data which is then encoded with the outer code, may furtherhave comprise the steps of performing error detection for a decoderesult in accordance with the error detecting code after frame dataobtained by decoding in accordance with the inner code is decoded inaccordance with the outer code; and transmitting a retransmission orderfor applicable frame data in accordance with an error detection resultin the step of performing error detection.

A wireless communication system according to another embodiment of thepresent invention includes a transmitter and a receiver. After encodingframe data with an outer code, the transmitter divides the frame datainto predetermined number of blocks which are further encoded with aninner code, and the transmitter transmits the encoded data to thereceiver by wireless. The receiver receives the transmitted data, storesthe received data in a buffer, decodes transmission data stored in thebuffer in accordance with the inner code, creates frame data bycombining the decoded blocks, decodes the frame data in accordance withthe outer code, outputs a decode result and likelihood informationthereof (decoded soft-decision value), determines whether or not toperform a retransmission order in units of blocks based on thelikelihood information, and transmits a retransmission order for anapplicable block if it is determined that a retransmission is necessarybased on the determining whether or not to perform a retransmissionorder, and in the case of determining whether or not to perform aretransmission order, the receiver inhibits the retransmission order forthe block if the number of inner-code errors in a frame composed of thepredetermined number of blocks stays within a limit of what the outercode can correct and determines that a retransmission is necessary ifthe number of inner-code errors in the frame exceeds the limit.

The present invention further provides a receiver and a transmitter inthe wireless communication system.

According to the present invention, since the error correctioncapability of the outer code is incorporated into retransmissionordering for an inner-code block, efficient retransmission orders can beperformed in a communication system that contains the outer and innercodes.

Further, performing the retransmission order employing inner-codedecoded likelihood negates the need to add an error detecting code forthe inner code.

Furthermore, determining the retransmission order for the inner codeappropriately according to an error state of the outer code enablesoptimizing the retransmission order for the inner-code block andadjusting appropriately in such a manner that an incidence of anouter-code error accords with an operational target of datacommunication. Furthermore, in the case of performing the retransmissionorder for the outer code, the number of retransmissions of the outercodes of high retransmission overhead can be properly controlled. Thus,wireless communication resources can be used effectively.

Moreover, determining the retransmission order appropriately for eachinner-code block constituting a data frame can avoid the retransmissionof unnecessary inner-code blocks. Thus, wireless communication resourcescan be used effectively.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an exemplary configuration of atransmitter in a wireless communication system according to anembodiment of the present invention;

FIG. 2 is a block diagram showing an example of a receiver correspondingto the transmitter of FIG. 1;

FIG. 3 is a block diagram showing an exemplary configuration of thedecoder in the receiver shown in FIG. 2;

FIG. 4 is a diagram showing a calculation way of an evaluation value inan embodiment of the present invention;

FIG. 5 is a graph showing a relationship between the evaluation value ofFIG. 4 and the number of errors in a decoded block;

FIG. 6 is a flowchart showing an exemplary process of a retransmissionorder determining unit in a receiver shown in FIG. 2;

FIG. 7 is a diagram showing another calculation way of an evaluationvalue in an embodiment of the present invention;

FIG. 8 is a graph showing a relationship between the evaluation value ofFIG. 7 and the number of errors in a decoded block;

FIG. 9 is a block diagram showing an exemplary configuration of atransmitter for realizing a conventional retransmission scheme;

FIG. 10 is a block diagram showing an exemplary configuration of areceiver, which corresponds to the transmitter of FIG. 9, for realizinga conventional retransmission scheme;

FIG. 11 is a block diagram showing an exemplary configuration of aconventional transmitter that uses a scheme for performing errorcorrecting doubly;

FIG. 12 is a block diagram showing an exemplary configuration of areceiver corresponding to the transmitter of FIG. 11; and

FIG. 13 is a diagram showing schematically a relationship between framedata and divided blocks in the transmitter of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of preferred embodiments of thepresent invention.

FIG. 1 is a block diagram showing an exemplary configuration of atransmitter 100 in a wireless communication system according to anembodiment of the present invention.

A transmitter 100 includes a retransmission buffer 101, an errordetecting code unit 102, an encoder 103 (by an outer code), a framedividing unit 104, a retransmission buffer 110, an encoder 105 (by aninner code), a modulator 106, a transmitting/receiving unit 107, ademodulator 108, and a retransmission controller 109. Although the basicconfiguration of the transmitter 100 is similar to that of thetransmitter 500 in FIG. 11, the transmitter 100 is different from thetransmitter 500 in that the second retransmission buffer 110 for storingthe divided data is provided besides the retransmission buffer 101 forstoring the user data and the retransmission controller 109 controlsboth the retransmission buffers 101 and 110. The configuration andoperation of the transmitter 100 in FIG. 1 will be described below.

New user data to be transmitted is temporarily stored in theretransmission buffer 101. If data to be transmitted is new data, thetransmitter 100 transmits the stored data. If data to be transmitted isretransmission data, the transmitter 100 transmits the past stored data.The error detecting code unit 102 adds an error detecting code (such asCRC) to transmission data. The encoder 103 encodes the transmission datato which the error detecting code is added, using an error correctingcode of an outer code. A Reed-Solomon code, a Bose-Chaudhuri-Hocquenghemcode (BCH code), etc. are used as the outer code. The data encoded bythe encoder 103 is divided into M blocks at a frame dividing unit 104.The retransmission buffer 110 stores each of the divided data pieces. Inaccordance with control of the retransmission controller 109, theretransmission buffer 110 outputs the stored data blocks. The encoder105 encodes each of the divided data pieces from the retransmissionbuffer 110 using a second error correcting code of an inner code. Aconvolutional code, a turbo code, etc. are used as the inner code. Thedata encoded by the encoder 105 is modulated by a modulator 106, and themodulated data is transmitted to a transmission line through atransmitting/receiving unit 107. The data received by thetransmitting/receiving unit 107 is demodulated by the demodulator 108,and the resulting data is sent to the retransmission controller 109.

The retransmission controller 109 discriminates between an inner-coderetransmission and an outer-code retransmission, and transmits the datastored in the retransmission buffer 110 in the case of the inner-coderetransmission. In the case of the outer-code retransmission, the datastored in the retransmission buffer 101 is transmitted. If ACK isobtained for an inner-code block, the retransmission controller 109clears the corresponding data in the retransmission buffer 110. If ACKis obtained for outer-code frame data, the retransmission controller 109clears the corresponding data in the retransmission buffer 101.

FIG. 2 shows an example of a receiver 200 corresponding to thetransmitter 100 of FIG. 1.

The receiver 200 includes a transmitting/receiving unit 201, ademodulator 202, a composition buffer 210, a decoder 203, a framecombining unit 204, a decoder 205, an error detector 207, aretransmission order controller 208, a modulator 209, and aretransmission order determining unit 211. Although the configuration ofthe receiver 200 is similar to that of the receiver 600 shown in FIG.12, the receiver 200 is different from the receiver 600 in that thecomposition buffer 210 is provided after the demodulator 202 and alsothe retransmission order determining unit 211 is added.

The transmission data received by a transmitting/receiving unit 201 isdetected and demodulated by a demodulator 202. The composition buffer210 stores each of the inner-code blocks demodulated. In the case ofretransmission data, the past stored data is added to the retransmissiondata and the added data is stored in the composition buffer 210. Thedecoder 203 decodes each of the divided data blocks outputted from thecomposition buffer 210. The decoder 203 outputs likelihood informationon each data bit of the decode result to the retransmission orderdetermining unit 211 in a manner described later. The frame combiningunit 204 combines M blocks of the data decoded by the decoder 203 andcreates a data frame which is decoded at a decoder 205. The errordetector 207 determines whether there is an error in the decoded datausing the error detecting code. If there is no error, the error detector207 outputs the decoded data as user data. The retransmission ordercontroller 208 creates ACK if the error detector 207 determines thatthere is no error, or NACK if the error detector 207 detects an error.The modulator 209 modulates a retransmission control message receivedfrom the retransmission order controller 208, and thetransmitting/receiving unit 201 transmits the message. A detaileddescription will be made later as to functions of the retransmissionorder determining unit 211 which is a characteristic function unit inthis embodiment.

FIG. 3 is a block diagram showing an exemplary configuration of thedecoder 203. This is an example in the case of using a turbo code withR=1/3. Since the configuration and operation themselves are alreadyknown, a description thereof is omitted here.

The retransmission order determining unit 211 has the followingfunctions.

(a) The retransmission order determining unit 211 derives evaluationvalues based on the likelihood information received from the decoder 203in a manner shown in FIG. 4. An average value of absolute values of thelikelihood information (decoded soft-decision values) within a block isused as an evaluation value. A correlation between the evaluation valueand the number of errors in a decoded block is shown by a graph in FIG.5. The horizontal axis of the graph denotes the number of error bits ina code block. The vertical axis denotes an average amplitude ofsoft-decision output values in a code block, that is, the evaluationvalue. “Eb/No” in FIG. 5 denotes a ratio of power density versus noisepower density per bit in a digitally modulated signal. The graph showsthat the number of errors decreases as the evaluation value increases.Therefore, it is possible to estimate whether or not the number oferrors in the inner code is within error correction capability of theouter code based on this correlation.

The retransmission order determining unit 211 determines a thresholdvalue TH[0] for the evaluation value as to whether or not to perform aretransmission order for an inner-code block in the following wayaccording to the error correction capability of the outer code. If theerror correction capability of the outer code can correct N errors, thenumber of errors allocated to each inner code is N/M (M refers to thenumber of blocks divided from a frame as described above). In accordancewith the relationship of FIG. 5, the evaluation value corresponding toN/M is determined to be the threshold value:TH[0]=func_map(N/M)  (1)where “func_map( )” is a function derived from the relationship of FIG.5 and outputs a value on the y-axis when an argument is a value on thex-axis. In reality, this is prepared with a data table, for example.

Comparing the evaluation value with the threshold value, if theevaluation value is not more than the threshold value, theretransmission order determining unit 211 performs the blockretransmission order (NACK). If the evaluation value is not less thanthe threshold value, the retransmission order determining unit 211determines that the data has been received correctly (ACK), and the datadecoded by the decoder 203 is outputted to the frame combining unit 204.

(b) In order to maintain retransmission orders for the outer-code dataat a constant rate, a threshold adjustment may be made to a decoded unit(each data frame code) of the outer code in the following manner.

In the case where there is an error at the outer code:TH[t]=TH[t−1]+(1−targetError)*adjust  (2)In the case where there is no error at the outer code:TH[t]=TH[t−1]−targetError*adjust  (3)where “t” is an integral parameter indicating a time lapse according toa data frame, and “targetError” is a target value (a positive numberless than 1) for the rate at which the retransmission order is performedin units of outer codes and a network operational parameter, and“adjust” is a predetermined threshold adjustment.

Equation (2) means that the block retransmission order occurs easily byraising the threshold value in the case where there is an error at theouter code. Equation (3) means that the block retransmission orderoccurs hard by lowering the threshold value in the case where there isno error at the outer code.

(c) In the case where the past block likelihood is high, it isacceptable that the likelihood required for the next block is low.Therefore, a threshold adjustment may be made in the following manner inaccordance with an inner-code block number (m) constituting anouter-code data frame.

The number of block errors in a data frame is obtained on the basis ofequation (4):

$\begin{matrix}{{{total\_ est}{{\_ error}\lbrack m\rbrack}} = {\sum\limits_{i = 1}^{m}{{est\_ error}\lbrack i\rbrack}}} & (4)\end{matrix}$

As shown by equation (5), an initial value of the threshold adjustmentΔth[m] for each inner-code block in the data frame is set to zero. Thethreshold adjustment Δth[m] is updated by updating the number of errors(N/M) allocated to each inner code for the initial threshold valueTH[0], in consideration of the number of accumulated errors(total_est_error [m]) in the data frame. The number of errors(est_error[m]) refers to the number of error bits on the horizontal axisthat the calculated evaluation value on the vertical axis of the graphin FIG. 5 is converted into.Δth [m]=0 for m=0Δth[m]=TH[0]−func_map((N−total_est_error[m])/(M−m)) elsewise  (5)

With a value obtained by multiplying the updated threshold adjustmentΔth[m] by a predetermined coefficient “alpha” (a positive number notmore than 1), the threshold value TH[t,m] for each inner-code block isupdated as shown by equation (6). The updating is performed bydecreasing the initial threshold value of the frame TH[t, 0] inaccordance with Δth[m].TH[t,m]=TH[t, 0]−alpha*Δth[m]  (6)

If there are few inner-code errors at early time in the frame, theouter-code error correction can cover them even in the case of loweringthe frequency of occurrence of the block retransmission order;therefore, the margin can be delivered to the subsequent block in theframe. That is, for the subsequent block, the threshold value is loweredso that ACK occurs easily and the block retransmission order occurshard.

FIG. 6 is a flowchart showing an exemplary process of the retransmissionorder determining unit 211. First, the retransmission order determiningunit 211 assesses the error correction capability of the outer code(S11). This corresponds to the foregoing correction capability for Nerrors. Next, the initial threshold value (TH [0]) is determined withequation (1) (S12).

Next, the process moves to processing of each outer-code frame (S13 toS26). In the processing of each outer-code frame, the retransmissionorder determining unit 211 checks for the presence or absence of anerror in the frame data (S14). If there is an error in the frame data,the threshold value TH is updated with equation (2) (S16). If there isno error in the frame data, the threshold value TH is updated withequation (3) (S15).

Next, the process moves to processing of each inner-code block (S17 toS25). First, there transmission order determining unit 211 estimates“total_est_error[m]” as shown by equation (4) (S18), and determines thethreshold value TH [t,m] according to equations (5) and (6) (S19).

Next, the retransmission order determining unit 211 calculates theevaluation value (S20), and compares the calculated evaluation valuewith the threshold value TH[t,m] (S21). If the evaluation value is lessthan the threshold value, the block retransmission order (NACK) isperformed (S23). If the evaluation value is equal to or more than thethreshold value, ACK is performed and the block retransmission order isnot performed (S22), and the composition buffer is cleared (S24). Theprocess of S18 to S24 is repeated for each inner-code block.

The process of FIG. 6 is an example into which all of the functions (a),(b), and (c) of the retransmission order determining unit 211 arecombined. Instead of this, only function (a), a combination of functions(a) and (b), and a combination of functions (b) and (c) may be employed.

The evaluation value has been determined in the manner shown in FIG. 4;however, this can be done in a manner shown in FIG. 7. That is, absolutevalues of the likelihood information (decoded soft-decision values) arecompared to a specified threshold value, and the total number ofabsolute values not more than the threshold value is determined to be anevaluation value.

In this case, a relationship between the evaluation value and the numberof errors in a decoded block is shown by a graph in FIG. 8. The graphshows the relationship that the number of errors in a block decreases asthe evaluation value decreases. In the case of using the evaluationvalue as described, the operation of the retransmission orderdetermining unit 211 is basically the same. However, since thecorrelation turns positive from negative, equations (2), (3), and (6)need to be changed to equations (2)′, (3)′, and (6)′ respectively.TH[t]=TH[t−1]−(1−targetError)*adjust  (2)′TH[t]=TH[t−1]+targetError*adjust  (3)′TH[t,m]=TH[t, 0]+alpha*Δth[m]  (6)′

In the foregoing, the detailed description has been made of thepreferred embodiments of the present invention, but variousmodifications and changes can be made besides the above-describedembodiments. For example, since some systems can tolerate errors presentin the error detector 207 in FIG. 2, it is not necessarily essential inthe present invention that the retransmission order controller 208creates the retransmission order in units of data frames.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A retransmission ordering method in a receiver for receivingtransmission data by wireless, frame data being encoded with an outercode and then divided into predetermined number of blocks which areencoded with an inner code into the transmission data, theretransmission ordering method comprising the steps of: receivingtransmission data; storing received transmission data in a buffer;decoding the transmission data stored in the buffer in accordance withthe inner code and outputting a decode result and likelihood informationthereof; creating frame data by combining decoded blocks; decoding theframe data in accordance with the outer code; determining whether toperform a retransmission order in units of blocks based on thelikelihood information; and transmitting a retransmission order for anapplicable block if it is determined that a retransmission is necessaryaccording to the step of determining whether to perform a retransmissionorder, wherein at the step of determining whether to perform aretransmission order, the retransmission order for the block isinhibited if the number of inner-code errors in a frame consisting ofthe predetermined number of blocks stays within a limit of what theouter code can correct and it is determined that a retransmission isnecessary if the number of inner-code errors in the frame exceeds thelimit.
 2. The retransmission ordering method according to claim 1,wherein the step of determining whether to perform a retransmissionorder comprises the steps of: finding an average value of absolutevalues of the likelihood information within a block as an evaluationvalue; and determining whether the block needs to be retransmitted bycomparing the evaluation value with a predetermined threshold value. 3.The retransmission ordering method according to claim 2, wherein anevaluation value corresponding to the number of errors N/M allocated toeach inner code is the predetermined threshold value in the case whereerror correction capability of the outer code can correct N errors andone piece of frame data is divided into M pieces.
 4. The retransmissionordering method according to claim 3, an error detecting code beingadded to the frame data which is then encoded with the outer code, theretransmission ordering method further comprising the steps of:performing error detection for a decode result in accordance with theerror detecting code after frame data obtained by decoding in accordancewith the inner code is decoded in accordance with the outer code; andchanging the predetermined threshold value in units of data frames sothat the retransmission order for the block occurs if an error isdetected in the step of performing error detection and in such a waythat the retransmission order for the block occurs if no error isdetected.
 5. The retransmission ordering method according to claim 3,further comprising the step of: changing the predetermined thresholdvalue in units of blocks in a data frame using a threshold adjustmentupdated by updating the number of errors N/M allocated to each innercode based on the number of accumulated errors as to sequential blocksin one data frame.
 6. The retransmission ordering method according toclaim 1, wherein the step of determining whether to perform aretransmission order comprises the steps of: finding the number of bitsthat lead to absolute values of the likelihood information that are notmore than a specified threshold value, as an evaluation value; anddetermining whether the block needs to be retransmitted by comparing theevaluation value with a predetermined threshold value.
 7. Theretransmission ordering method according to claim 6, wherein anevaluation value corresponding to the number of errors N/M allocated toeach inner code is the predetermined threshold value in the case whereerror correction capability of the outer code can correct N errors andone piece of frame data is divided into M pieces.
 8. The retransmissionordering method according to claim 1, an error detecting code beingadded to the frame data which is then encoded with the outer code, theretransmission ordering method further comprising the steps of:performing error detection for a decode result in accordance with theerror detecting code after frame data obtained by decoding in accordancewith the inner code is decoded in accordance with the outer code; andtransmitting a retransmission order for applicable frame data inaccordance with an error detection result in the step of performingerror detection.
 9. A wireless communication system comprising atransmitter and a receiver, wherein after encoding frame data with anouter code, the transmitter divides the frame data into predeterminednumber of blocks which are further encoded with an inner code, and thetransmitter transmits the encoded data to the receiver by wireless; andwherein the receiver receives transmitted data, stores received data ina buffer, decodes transmission data stored in the buffer in accordancewith the inner code, creates frame data by combining decoded blocks,decodes the frame data in accordance with the outer code, outputs adecode result and likelihood information thereof, determines whether toperform a retransmission order in units of blocks based on thelikelihood information, and transmits a retransmission order for anapplicable block if it is determined that a retransmission is necessarybased on the determining whether to perform a retransmission order, andin the case of determining whether to perform a retransmission order,the receiver inhibits the retransmission order for the block if thenumber of inner-code errors in a frame consisting of the predeterminednumber of blocks stays within a limit of what the outer code can correctand determines that a retransmission is necessary if the number ofinner-code errors in the frame exceeds the limit.
 10. A receiver forreceiving transmission data by wireless, frame data being encoded withan outer code and then divided into predetermined number of blocks whichare encoded with an inner code into the transmission data, the receivercomprising: a buffer for storing received transmission data; firstdecoding means for decoding the transmission data stored in the bufferin accordance with the inner code and outputting a decode result andlikelihood information thereof; frame combining means for creating framedata by combining decoded blocks; second decoding means for decoding theframe data in accordance with the outer code; retransmission orderdetermining means for determining whether to perform a retransmissionorder in units of blocks based on the likelihood information from thefirst decoding means; and retransmission order transmitting means fortransmitting a retransmission order for an applicable block if theretransmission order determining means determines that a retransmissionis necessary, wherein the retransmission order determining meansinhibits the retransmission order for the block if the number ofinner-code errors in a frame consisting of the predetermined number ofblocks stays within a limit of what the outer code can correct at thesecond decoding means and determines that a retransmission is necessaryif the number of inner-code errors in the frame exceeds the limit. 11.The receiver according to claim 10, wherein the retransmission orderdetermining means comprises: means for finding an average value ofabsolute values of the likelihood information within a block as anevaluation value; and means for determining whether the block needs tobe retransmitted by comparing the evaluation value with a predeterminedthreshold value.
 12. The receiver according to claim 10, wherein theretransmission order determining means comprises: means for finding thenumber of bits that lead to absolute values of the likelihoodinformation that are not more than a specified threshold value, as anevaluation value; and means for determining whether the block needs tobe retransmitted by comparing the evaluation value with a predeterminedthreshold value.
 13. The receiver according to claim 11, wherein anevaluation value corresponding to the number of errors N/M allocated toeach inner code is the predetermined threshold value in the case whereerror correction capability of the outer code can correct N errors andone piece of frame data is divided into M pieces.
 14. The receiveraccording to claim 13, an error detecting code being added to the framedata which is then encoded with the outer code, the receiver furthercomprising: error detecting means for performing error detection inaccordance with the error detecting code; and first threshold changingmeans for changing the predetermined threshold value in units of dataframes in such a way that the retransmission order for the block occursif the error detecting means detects an error and in such a way that theretransmission order for the block occurs if the error detecting meansdetects no error.
 15. The receiver according to claim 13, furthercomprising second threshold changing means for changing thepredetermined threshold value in units of blocks in a data frame using athreshold adjustment updated by updating the number of errors N/Mallocated to each inner code based on the number of accumulated errorsas to sequential blocks in one data frame.
 16. The receiver according toclaim 12, wherein an evaluation value corresponding to the number oferrors N/M allocated to each inner code is the predetermined thresholdvalue in the case where error correction capability of the outer codecan correct N errors and one piece of frame data is divided into Mpieces.
 17. The receiver according to claim 10, an error detecting codebeing added to the frame data which is then encoded with the outer code,the receiver further comprising: error detecting means for performingerror detection in accordance with the error detecting code; andretransmission order controlling means for creating a retransmissionorder for applicable frame data in accordance with an error detectionresult by the error detecting means.